In modern photographic materials, it is known to incorporate development inhibitor compounds or compounds capable of releasing development inhibitors or precursors thereof, in order to arrest development and optimize certain photographic characteristics. Characteristics which may be impacted by the presence of development inhibitor compounds include sharpness, granularity, contrast and color reproduction.
In certain instances, it is often desired to coat a development inhibitor in one layer of the photographic element and have it exert its effects on adjacent or other layers. It is also often desired that development inhibitors not exert their effects during the initial stages of development but rather after extended development times. In such instances, it has become commonplace to alter the structure of development inhibitors so that they are inactivated by a blocking or timing group. The inactivated development inhibitors are then activated after either a period of exposure to compounds normally present in processing solutions, or after exposure to a specific compound capable of splitting-off the blocking or timing group.
Examples of photographic elements containing development inhibitor moieties can be found in U.S. Pat. Nos. 5,041,367, 3,397,987 and 4,886,738.
In U.S. Pat. No. 5,041,367, photographic recording materials are disclosed having improved sharpness and enhanced interlayer interimage effects. The recording materials comprise an unblocked 5- or 6-membered heterocyclic ring containing development inhibitor compound and a polymeric development accelerator compound.
In U.S. Pat. No. 3,397,987, photographic emulsions are described having unfogged surface latent image grains and fogged internal silver halide grains on which is adsorbed a heterocyclic nitrogen containing development fog inhibiting compound. The development fog inhibiting compound is free and is thus unblocked.
In U.S. Pat. No. 4,886,738, color photographic materials are disclosed having one of two types of development inhibitor compounds positioned in a colloidal silver containing layer. The development inhibitor compounds are adsorbed to the colloidal silver and gradually separate therefrom during development. After separation from the colloidal silver, the development inhibitor compounds diffuse into a photosensitive emulsion layer and impact such photographic properties as D.sub.max (i.e. maximum density on the emulsion's characteristic curve) and speed.
In U.S. Pat. No. 4,626,498, color reversal photographic light sensitive materials having a light sensitive silver halide emulsion layer and a layer adjacent thereto are disclosed. The layer adjacent to the emulsion layer contains an organic compound and silver halide grains containing internal fog centers. The organic compound may be a heterocyclic mercapto compound such as phenyl mercaptotetrazole. Such heterocyclic mercapto compounds are generally known in the art as unblocked development inhibitors.
In U.S. Pat. No. 5,354,650, blocked development inhibitor moieties are disclosed which provide, in an imagewise manner after reaction with a second compound that is photographically inert in the layer in which it is coated, or in the form in which it is released, a development inhibitor moiety.
In U.S. Ser. No. 08/250,148, filed May 27, 1994, release compounds are disclosed which provide a non-imagewise distribution of a photographically active moiety, of which development inhibitors are included. The release compounds comprise a blocking group from which the development inhibitor is released, a ballasting group other than a coupler moiety, which is attached to the blocking group, and an aqueous solubilizing group which is also attached to the blocking group.
One of the disadvantages associated with utilizing blocked development inhibitor moieties is that they often do not allow one to optimize photographic characteristics over a wide range of different photographic elements and processing conditions. For instance, in U.S. Pat. No. 5,354,650, release of the development inhibitor is only in an imagewise manner. Thus, non-imagewise control is lost.
By contrast, the release compounds of U.S. Ser. No. 08/250,148, filed May 27, 1994, can release development inhibitors in a non-imagewise manner, and as a result of exposure to nucleophiles normally present in the processing solutions. These release compounds provide excellent results when incorporated into reversal elements that are push processed. Push processing is a speed adjusting process utilized to compensate for insufficient exposure of one or more of the color records of a color reversal light sensitive material. Typically, it is accomplished by "pushing" the first of the development stages (i.e. black and white) of reversal processing; that is, it is accomplished by prolonging the period of first development longer than that employed in normal processing.
The release compounds of U.S. Ser. No. 08/250,148, filed May 27, 1994 are useful in elements that are push processed because they tend to release their development inhibitors after extended development times. Thus, they impact the characteristics of the photographic element primarily after the initial development phase. This allows one to affect color balance by slowing the development of one silver halide emulsion layer during the push phase while simultaneously allowing the other silver halide emulsion layers to continue developing without restraint.
Although some of the blocked or timed inhibitors known in the art are capable of impacting photographic properties primarily during the push phase of reversal processing, at certain levels or in certain photographic elements, they may also exert a small effect during the pre-push phase. This small effect, though often minimal, may be undesired as it can limit the ability of the release compounds to adequately impact speed and color correction. For this reason, it is desired to provide a photographic element containing blocked development inhibitors wherein the impact of the development inhibitors, once released, is minimized during the pre-push phase of reversal processing and maximized during the push phase.
It is also desired to provide photographic elements that exhibit adequate sensitivity changes when subjected to development inhibitors that have been released from blocking groups.